Preparation of Polyamide‐6 Submicrometer‐Sized Spheres by In Situ Polymerization

Polyamide‐6 (PA6) submicron‐sized spheres are prepared by two steps: (1) anionic ring‐opening polymerization of ε‐caprolactam in the presence of poly(ethylene glycol)‐ block ‐poly‐(propylene glycol)‐ block ‐poly(ethylene glycol)(PEG‐ b ‐PPG‐ b ‐PEG) and (2) separation of PA6 spheres by dissolving PEG‐ b ‐PPG‐ b ‐PEG from the prepared blends. The PA6 microspheres obtained are regular spherical, with diameter ranging from 200 nm to 2 μm and narrow size distribution, as confirmed by scanning electron microscopy. By comparison with PA6/PS and PA6/PEG systems, it is denominated that the PEG blocks in PEG‐ b ‐PPG‐ b ‐PEG can effectively reduce the surface tension of PA6 droplets and further decrease the diameter of the PA6 microspheres. The PPG block in PEG‐ b ‐PPG‐ b ‐PEG can prevent the PA6 droplets coalescing with each other, and isolated spherical particles can be obtained finally. The phase inversion of the PA6/PEG‐ b ‐PPG‐ b ‐PEG blends occurs at very low PEG‐ b ‐PPG‐ b ‐PEG content; the PEG‐ b ‐PPG‐ b ‐PEG phase can be removed by water easily. The whole experiment can be finished in a short time (approximately in half an hour) without using any organic solvents; it is an efficient strategy for the preparation of submicron‐sized PA6 microspheres.